The invention relates to the employment of glassy, photoresponsive polymeric materials as optically fixable shape memory polymers in which the shape fixing mechanism is due to non-reactive, photoinduced reconfigurations of the polymer network morphology.
Shape memory polymers (SMPs) are stimuli-responsive materials that remember an original, so-called “permanent shape” that can be recovered from a temporary fixed shape by exposure to external stimuli such as heat, electricity, moisture, solvent, or magnetic field. Shape fixing is most commonly observed by heating the polymeric material above a transition temperature, which can be the glass transition (Tg), melting (Tm), or a crystalline clearing temperature (Tcl). Recent work in the area has demonstrated polymeric materials with multiple transitions can exhibit two-way shape memory (2W-SM) behaviour and so-called triple shape memory in systems possessing both chemical and physical crosslinking. Realization of multiple temporary shapes is critical to the employment of SMP in more complex applications.
Only a few patents/publications address what has been previously referred to as light-activated shape memory. Directing shape adaptations with light equips a potential user with remote, wireless control in addition to the potential for spatial control with masking or holographic exposure. Both prior reports of light-activated SMP leverage photoinduced changes to the crosslink density of the network to program and release a desired shape. One prior report specifies their system as composed of an interpenetrating network containing up to 10 mol % of cinnamic acid groups, which photocrosslink when subjected to UV light >260 nm for one hour to “photo-fix” a mechanically elongated shape. Subsequent irradiation with UV light <260 nm for one hour decrosslinks and releases the fixed shape. Fixity, a fractional measure of the extent of shape/strain retention, was reported in the range of 0.3-0.5.